Hydrogen purification using molecular dynamics

ABSTRACT

A membrane is described for purifying or separating hydrogen from a multi-component gas stream such as syngas. This membrane uses a molecular pre-treatment, a transition metal, fluorine containing polymer, carbon fibers and carbon matrix sintered on a supportive screen. The membrane may be a bilayer membrane comprised of a layer containing high surface area carbon and another layer containing lower surface area carbon. Methods for purifying hydrogen are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 17/389,014, filed on Jul. 29, 2021, which claimspriority to U.S. Provisional Patent Application No. 63/061,608, filedAug. 5, 2020, the contents of which are incorporated in theirentireties.

TECHNICAL FIELD

The disclosure broadly relates to hydrogen production, and moreparticularly, to a membrane capable of selectively filtering outhydrogen from natural, renewable or trace gas sources.

BACKGROUND

Hydrogen is an energy carrier and is becoming more viable as an energysource at the consumer level. The hydrogen industry is moving at anever-increasing pace towards lower cost production and commercializationin a global environment. Successful hydrogen commercialization willrequire production from renewable energy sources and distribution thatis competitive or lower cost than other energy resources.

Hydrogen use does not produce carbon emissions when used as an energysource in a fuel-cell application or as the fuel in an internalcombustion engine or vehicle. Current commercial production of hydrogenis achieved with steam gasification of methane that releases copiousamounts of carbon into the atmosphere, which is referred to as “grayhydrogen.” A lower carbon footprint production of hydrogen uses CarbonCapture and Sequestration (CCS), which is referred to as “bluehydrogen.” The zero-carbon footprint production is derived viaelectrolysis or splitting of water using renewable energy, which isreferred to as “green hydrogen.”

As costs of renewable energy decrease, significant quantities ofhydrogen will be produced for the consumer in a projected price range of$1 to $2 per kg, making hydrogen competitive with gasoline or naturalgas on an energy equivalent basis. Hydrogen is also complementary tofuel cell electric vehicles.

Hydrogen purification is currently commercially attained at scale bypressure swing adsorption and cryogenic distillation. Both of thesetechniques require significant energy expenditures and substantialcapital expense. A more viable approach might entail the use of amembrane system which incorporates minimal capital expense, low carbonfootprint, and operational flexibility while meeting the volumethroughput of current and future commercial applications.

SUMMARY

As disclosed herein, the present disclosure solves the above-describeddisadvantages by providing a membrane system which incorporates minimalcapital expense, low carbon footprint, and operational flexibility whilemeeting the volume throughput of current and future commercialapplications. In particular, if hydrogen is transported in existingnatural gas lines as is now being proposed globally, with a 5 to 20%hydrogen to natural gas ratio contained in the pipeline, a separatingmembrane to extract this hydrogen from the other gasses would slash boththe carbon footprint and the user's hydrogen cost. This hydrogenseparating membrane would accelerate achieving a zero-carbon energysociety.

Membrane gas separation could have a significant impact on commercialhydrogen production, in particular as it relates to using a passive,selectively engineered permeable, polymer membrane that is pre-treated,to produce a highly purified hydrogen derived from renewable sources.Currently commercially available membranes are based on precious metals.Specifically, membranes are typically coated with palladium 20 to 50microns in thickness. These membranes are expensive due to the high costof the underlying palladium or platinum group metals (PGM's) as well asthe high cost of the membrane fabrication. Additionally, issues such ashydrogen embrittlement of these precious metals limit the life of thesemembranes.

Hydrogen purification membranes comprised of inexpensive materialsproduced by simple manufacturing process are needed. One alternative ispolymeric membranes comprised of a support layer, and a selectivepermeable polymer layer residing on the support layer. Typically, thesepolymer membranes are very thin, on the order of 1 to 5 microns, andconsist of such polymers as ethyl cellulose and polydimethylsiloxane.These membranes are not currently a commercial product and are presentlylimited by the volume of material that can be processed per unit time.

Embodiments of the present application disclose a multi-stage hybridmembrane comprising carbon, fluorine containing polymer and is without(PGM) metal. This membrane effectively filters out hydrogen whenpre-treated by gas molecules from a gas stream containing a variety ofother gases, in particular gases that include methane, and carbondioxide from the gas origin.

Prior work in this area includes U.S. Pat. No. 5,432,022, describing acoated cathode for a rechargeable metal battery in which a metal-airbattery is protected against the effects of CO₂ by incorporating a CO₂gettering agent which is embedded in a hydrophobic binder material toform a gas-permeable layer deposited on the current collector. Thispatent fails to mention utility with regard to hydrogen selectivity anduse as a hydrogen purification membrane. U.S. Pat. No. 9,358,506 toCheiky refers to a hydrogen separation system and membrane forextracting hydrogen from gasifier streams at near atmospheric pressureand ambient temperature conditions. The system comprises a bypass valvedisposed between the gasifier and the engine genset for routing the gasstream through a hydrogen concentrator; and the hydrogen concentratorfor concentrating the gas stream, the hydrogen concentrator comprising afilter for filtering the gas stream, a pump for pumping the gas streamthrough the hydrogen concentrator, a membrane formed from a bulk carbonwhich is compressed and held in form by sintered PTFE, and a hydrogencompressor; wherein the membrane comprises a permselective membrane forpermeating hydrogen from the gas stream.

Embodiments of the present application differ from this prior work inthe construction of the membrane, in the pre-treatment membrane process,and uses a transition metal compound in one or more layers, one layercomprising a high surface area carbon, and other layers comprising alower surface area carbon. A full differentiation will be apparent fromthe detailed description of this invention.

Some embodiments of the present disclosure are directed toward amembrane or membrane system capable of concentrating and purifyinghydrogen from a gas stream comprised of a variety of manmade or naturalgases, such as nitrogen, carbon dioxide, oxygen, carbon monoxide andmethane. Certain embodiments utilize gas streams derived from steamgasification of natural gas, while other embodiments utilize a gasstream derived from using renewable energy for electrolysis of water,gas streams from abandoned and uncapped hydrocarbon wells, biomethanefrom mammalian and bacterial emissions as broken down in a biodigester.The membrane system described herein is comprised of at least onemembrane exhibiting special selectivity towards hydrogen with amolecular conditioned gas pre-treatment for selective permeabilityrelative to other components in the gas stream.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the present disclosure will hereinafter bedescribed in detail, by way of example only, with reference to theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view illustrating the construction of amembrane systems, in accordance with embodiments of the presentapplication.

FIG. 2 is a diagram illustrating an experimental setup to characterizethe selectivity of various membranes, in accordance with embodiments ofthe present application.

FIG. 3 is a table illustrating the results of permeability runs fordifferent membranes built in accordance with the methods disclosedherein.

FIG. 4 a hydrogen concentrator that incorporates membranes builtaccording to the methods disclosed herein.

FIGS. 5 and 6 are diagrams illustrating the differences in hydrogen andCO₂ kinetic diameters, in accordance with embodiments of the presentapplication.

The figures are not intended to be exhaustive or to limit the disclosureto the precise form disclosed. It should be understood that thedisclosure can be practiced with modification and alteration, and thatthe disclosure be limited only by the claims and the equivalentsthereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to FIG. 1 , membrane system 5 is comprised of at least oneactive hydrogen transporting layer. Although the depicted embodimentcontains two layers, any number of layers is possible without departingfrom the scope of the present application. Layer 30 is a comprised ofmaterials containing a mixture of carbon fibers, transition nonmetalcompounds, a fluorine containing polymer, and activated carbon. Layer 20is comprised of a mixture of carbon fibers, transition metal compounds,a fluorine containing polymer, and low porosity carbon. Both substratesare supported by a metal or Kevlar screen or other structural supportwhich permits the free flow of gasses 10.

Screen 10 can be a porous filter made from a variety of differentmaterials whose primary purpose is to provide mechanical strength to themembrane while allowing significant flow of incoming gas. This layer maybe a glass fiber filter, Kevlar, metal screen filter, ceramic filter,polyester filter, or polypropylene filter. It may also comprisemechanically strong microporous filters such as built from nylon,polysulfone, Kevlar, polyvinylidene fluoride, andpolytetrafluoroethylene (PTFE). In some embodiments, the screencomprises a ceramic filter, which can have pore sizes as small as 0.1microns.

Layer 20 can comprise a more permeable and open structure than layer 30due to inclusion of lower density carbon materials. The carbon used inthis construction may be a number of carbon blacks such as thermallydecomposed carbon from petroleum sources (e.g., pet coke, acetylene ornatural gas). It may also comprise carbon materials such as carbonnanotube, carbon nanofiber and graphene. Typical dimensional spacing ofthis carbon material are less than 200 nm, and spaces between carbonparticles smaller than 300 m²/g are preferred embodiments. This layerhas a more open structure than layer 30 and allows for a prefilteringand faster throughput of material.

In some embodiments, layer 30 is substantially similar in materialcomposition but differs in construction of layer 20 in the nature of thecarbon and the transition metal compound used. Layer 30 uses activatedcarbon with porosities exceeding 300 m²/g, and preferably exceeding 500m²/g, and more preferably exceeding 700 m²/g. This activated carbon maybe derived from a variety of different sources, including, but notlimited to, coconut shells, almond shells, wood, biomass trimmings, andcoal. These activated carbons typically have nanopores less than 3 nm indiameter. The specific surface area herein is determined by measuringthe nitrogen or carbon dioxide adsorption amount and using a BrunauerEmmet and Teller (BET) method. Micropores, i.e. pores in the micronrange, may be built into this membrane through the use of pore formingmaterials such as ammonium carbonate.

Proper porosity in combination with molecular pre-treating of themembrane are believed to be responsible for the observed selectivity inthe membranes. A transition metals compound can be added to aid thegettering power of the membrane towards methane while slowing down theCO₂ flow through. The transition metal compounds in these membranes maycomprise a compound of nickel, cobalt, titanium, tungsten, vanadium,chromium, manganese, iron, copper, zinc, zirconium, molybdenum, silver,or niobium, as a salt of such as hydroxide, carbonate, chloride,nitrate, nitrite, or sulfate, or as an organometallic complex catalyst.Examples of these organometallic compounds of nickel, cobalt, titanium,or iron may include acetylacetonate compounds, salts of carboxylic acid,and cyclopentadienyl compounds of each of the metals.

The carbon powders used in the membranes of the current disclosure arepreferably embedded in a matrix of a fluorine-containing polymer such aspolytetrafluoroethylene (PTFE), poly(trifluoro ethylene), poly trifluorochloroethylene, polyvinyl fluoride, or any compound bearing the formulaC_(x)H_(y)F_(z) or C_(x)H_(y)F_(z)O_(a), or polymers thereof, where x,y, z and a are positive integers or 0. Other hydrocarbons that may beutilized include polypropylene and polyethylene.

The following example illustrates the construction of this membranesystem.

Example 1

HIGH SURFACE AREA LAYER: 0.25 g of carbon fibers of length 3 mm aremixed with 200 mL of methanol to form a slurry and 3 g of 1000 m²/gactivated carbon are added to mixture and blended in a mechanicalstirrer. 7 g of PTFE suspension along with 1 g of cobalt hydroxide aresubsequently added to the mixture. The entire well mixed contents areadded to a filter bed containing the support screen. The bed assemblyallows the removal of the methanol upon vacuum application to leave asolid cake.

LOWER SURFACE AREA LAYER: 0.25 g of carbon fibers of length 3 mm aremixed with 200 ml of methanol to form a slurry and 3 g of 40 m²/g carbonblack are added to mixture and blended in a mechanical stirrer. 3.5 g ofPTFE suspension along with 1 g of nickel hydroxide are subsequentlyadded to the mixture.

The entire well mixed contents of the lower surface area layer are addedto the high surface area cake material, and the methanol is subsequentlyextracted with vacuum to leave the bilayer cake. The solid cake isslowly heated below the boiling point of methanol to remove most of anyresidual solvent. The dry cake is subsequently placed between two metalplates and the assembly is sintered while at high pressure to atemperature of 350° C. where the polymer is rendered completelythermoset.

FIG. 2 is a diagram illustrating an experimental setup to characterizethe selectivity of various membranes, in accordance with embodiments ofthe present application. In particular, several membranes builtaccording to this protocol were tested for hydrogen selectivity in anassembly 200 as shown in FIG. 2 . This assembly 200 is comprised of ametal assembly divided into 2 fixtures, an upper fixture 210 and lowerfixture 220, separated by the test membrane 230. The membrane 230 isclamped down between the upper and lower fixtures in a leak proof mannerin order to permit the inlet gas stream 240 to pass only through themembrane. Both upper fixture 210 and lower fixture 220 contain samplingports 250, 260 to analyze the gas composition in each fixture. Analysisis performed using gas chromatography (GC) using a thermal conductivitydetector. The inlet gas was comprised of a mixture of methane, hydrogenand carbon dioxide. In a typical experiment run, the lower fixture 220is pressurized to 1 to 5 psi with the input gas stream while the upperfixture 210 is evacuated to remove all air. Hydrogen, due to its sizeand speed, is used to clean and condition the membrane 230. The CO₂ flowis admitted, and after a suitable time interval, for example from 30seconds to 20 minutes, the gas compositions in the upper and lowerfixtures is analyzed.

FIG. 3 is a table illustrating the results of permeability runs fordifferent membranes built according to the methods of the presentapplication. Shown are the ratios of hydrogen to carbon dioxide in theupper versus lower fixtures various times. The membranes observed showeda large average enhancement ratio greater than 40×, after 65 tests.Permeability was estimated as 388 cm³/cm²-min.

FIG. 4 illustrates a hydrogen concentrator system 400 that incorporatesmembranes built according to the method of the present application.Gases captured from hydrogen production are routed to one end of ahydrogen concentrator 410 containing multiple membranes at low pressure.As depicted, the input syngas in balloon 420 is heavier than air. Afterentering the concentrator 410, the output is sent to a pump forcompression prior to filling the airborne balloon 440. This figureillustrates the purification of the membranes of the present disclosure.

Referring to FIGS. 5 and 6 , there are differences in hydrogen and CO₂kinetic diameters (i.e., molecules are always flexing and rotating asthey move). In the illustrated example, CO₂ is the “test molecule” as itis only 41 picometers (10⁻¹² m) larger that hydrogen. The other CH₄ andCO molecules are much larger, such that good results with CO₂ will leadto even better results for separating the larger molecules (i.e., CH₄and CO).

Hydrogen moves @ ˜2000 m/s (over 1 mile/sec.), whereas CO₂ is muchslower @ ˜400 m/s. However, both have the same kinetic energy due totheir mass difference (light and fast for hydrogen versus heavy and slowfor CO₂). Keeping the hydrogen moving and pulsing in the other gasesallows the hydrogen to kinetically displace or “knock” the biggermolecules away from entering and clogging the small membrane openings atthe membrane composition and porous opening size distributions of thevarious membranes described herein.

Moreover, a larger pulse of CO₂ unexpectedly allows additional hydrogenthrough due to the fact that CO₂ selectively blocks the slightly largeropenings and pathways, as the smaller openings allow only hydrogen topass. This selective blocking or molecular sieving represents anexciting inverse effect due to the membrane composition. It is thenpossible to shut down or cut back the CO₂ so that the molecular sievingis restored in minutes.

While the application has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the embodimentsdisclosed herein are intended to cover such modifications as fall withinthe scope of the appended claims.

In the following paragraphs, embodiments of the present disclosure willbe described in detail by way of example with reference to the attacheddrawings. Throughout this description, the preferred embodiment andexamples shown should be considered as exemplars, rather than aslimitations on the present disclosure. As used herein, the “presentdisclosure” refers to any one of the embodiments of the disclosuredescribed herein, and any equivalents. Furthermore, reference to variousfeature(s) of the “present disclosure” throughout this document does notmean that all claimed embodiments or methods must include the referencedfeature(s).

One skilled in the art will appreciate that the present disclosure canbe practiced by other than the various embodiments and preferredembodiments, which are presented in this description for purposes ofillustration and not of limitation, and the present disclosure islimited only by the claims that follow. It is noted that equivalents forthe particular embodiments discussed in this description may practicethe disclosure as well.

While various embodiments of the present disclosure have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for thedisclosure, which is done to aid in understanding the features andfunctionality that may be included in the disclosure. The disclosure isnot restricted to the illustrated example architectures orconfigurations, but the desired features may be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations may be implementedto implement the desired features of the present disclosure. Also, amultitude of different constituent module names other than thosedepicted herein may be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Although the disclosure is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead may beapplied, alone or in various combinations, to one or more of the otherembodiments of the disclosure, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus, the breadth and scope of the presentdisclosure should not be limited by any of the above-described exemplaryembodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

A group of items linked with the conjunction “and” should not be read asrequiring that each and every one of those items be present in thegrouping, but rather should be read as “and/or” unless expressly statedotherwise. Similarly, a group of items linked with the conjunction “or”should not be read as requiring mutual exclusivity among that group, butrather should also be read as “and/or” unless expressly statedotherwise.

Furthermore, although items, elements or components of the disclosuremay be described or claimed in the singular, the plural is contemplatedto be within the scope thereof unless limitation to the singular isexplicitly stated.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, may be combined in asingle package or separately maintained and may further be distributedacross multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives may be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is:
 1. A method for hydrogen purification, comprising:providing a hydrogen comprising a multi-stage hybrid membrane, eachmembrane comprising a screen, a first layer formed on the screen and asecond layer formed on the first layer; pumping a gas stream through thehydrogen concentrator, the gas stream comprising syngas includinghydrogen and at least one additional gas; and separating hydrogen fromthe mixture containing hydrogen and the at least one additional gas;wherein pumping the gas stream comprises keeping the hydrogen movingwithin the hydrogen concentrator and pulsing in the at least oneadditional gas.
 2. The method of claim 1, further comprising forming thefirst layer from a mixture of carbon fibers, transition metal compounds,a fluorine containing polymer, and an additional carbon material.
 3. Themethod of claim 2, further comprising forming the second layer from amixture of carbon fibers, transition metal compounds, a fluorinecontaining polymer, and activated carbon.
 4. The method of claim 1,further comprising forming the first layer to be a more porous structurethan the second layer to provide prefiltering and faster throughput ofmaterial.
 5. The method of claim 1, further comprising forming the firstlayer from at least one lower density carbon material such that itcomprises a more permeable and open structure than the second layer. 6.The method of claim 5, wherein the at least one lower density carbonmaterial precursor is selected from the group consisting of: carbonnanotube, carbon nanofiber, carbon black derived from pet coke,acetylene or natural gas, and graphene.
 7. The method of claim 3,further comprising deriving the activated carbon from sources selectedfrom the group consisting of: coconut shells, almond shells, wood,biomass trimmings, and coal.
 8. The method of claim 1, furthercomprising pre-treating the membrane with gas molecules from a gasstream containing methane and carbon dioxide.
 9. The method of claim 1,wherein the at least one additional gas comprises carbon dioxide. 10.The method of claim 1, wherein the at least one additional gas comprisescarbon dioxide and methane.